1. Field of the Invention
The present invention relates to a temperature-sensitive color-memorizing microcapsulated pigment, more specifically, to a temperature-sensitive color-memorizing microcapsulated pigment which exhibits a wide hysteresis range of coloring/decloring alternately and reversibly caused by temperature changes and remains in the colored/decolored state at ambient temperatures without being continuously exposed to high/low temperatures required for causing the colored/decolored state.
2. Related Background Art
A temperature-sensitive color-memorizing microcapsulated material of the above-mentioned kind is disclosed in Japanese Patent Publication No. 4-17154. A widely-used, typical reversible thermochromatic material exhibiting thermochromatism at a certain color-change-causing temperature can be, at ambient temperatures, only in one of its two states, that is, in the state maintained at ambient temperature. The other state can not be maintained unless the material is continuously exposed to a temperature beyond the color-change-causing temperature in a case that the color-change-causing temperature is higher than ambient temperature, or to a temperature below the color-change-causing temperature in a case that the color-change-causing temperature is lower than ambient temperatures. The temperature-sensitive color-memorizing material disclosed in said patent publication, however, can selectively maintain, at ambient temperatures, both of its two states obtained at temperatures higher/lower than the color-change-causing temperature. By heating and cooling the material the two states can be alternately selected to be maintained at ambient temperatures. As a result, the temperature-sensitive color-memorizing material has been applied to various kinds of fields such as temperature-sensitive recording materials, toys, ornaments, printing materials, and so on.
As described in the Japanese Patent Publication No. 4-17154, the above-mentioned color-memorizing effect consists in thermochromism obtained only by systems having, as a constituent, compound(s) selected from a specific group of esters included in the group of esters used to control color forming reactions. In other words, the ester to be employed in the material can not be freely chosen and the applications of the temperature-sensitive color-memorizing material are limited. Accordingly, new materials of this kind which are more effective and more useful have been greatly demanded.